1. Field of the Invention
The invention relates to an onboard electronic device.
2. Description of Related Art
A hybrid vehicle (HV) is available in which a load factor limit of a boost converter is decreased as the temperature of a plurality of switching elements of the boost converter rises and also as the temperature of cooling water that cools the plurality of switching elements rises (see, for example, Japanese Patent Application Publication No. 2013-095147 (JP 2013-095147 A)).
However, since the switching elements of this type are typically joined by soldering, or the like, to a substrate, the switching elements are in contact with a coolant through a plurality of materials. Therefore, regarding heat generation by the switching elements, not only the heat resistance, but also thermal stresses caused by the difference in thermal expansion coefficient between the materials are problematic.
In this respect, since the only the heat resistance temperature of switching elements is considered in the configuration described in JP 2013-095147 A, fracture caused by thermal stresses can occur. For example, in the configuration described in JP 2013-095147 A, the temperature of the elements rises rather significantly when the cooling water temperature is low. However, where a comparatively large increase in the element temperature occurs, the difference between the thermal deformation amount of the switching elements and the thermal deformation amount of a material (solder, etc.) located below the switching elements increases, thereby increasing the-thermal stresses applied to the switching elements and the material. Those thermal stresses can fracture the switching elements.